Mineclonia/mods/MISC/mcl_anti_dimension_hopping/init.lua

local S = minetest.get_translator("mcl_anti_dimension_hopping")

local storage = minetest.get_mod_storage()

local MAX_DISTANCE = 40

local dimension_change_is_legal = function(
	player_name,		-- string
	dimension,		-- "end"|"nether"|"overworld"|"void"
	last_dimension,		-- "end"|"nether"|"overworld"|"void"
	last_last_dimension	-- "end"|"nether"|"overworld"|"void"|nil
)
	local player = minetest.get_player_by_name(player_name)
	if nil == player then
		return false
	end
	local player_position = player:get_pos()
	if "end" == dimension then
		assert( player_position.y > mcl_vars.mg_end_min )
		assert( player_position.y < mcl_vars.mg_end_max )
		-- Going to the End through a portal is allowed, but a
		-- player must appear at End spawn for it to be legal.
		-- The Nether as the last dimension is included here
		-- because an End portal in the nether sends players
		-- to End spawn, but cheaters can not teleport down
		-- from the Nether, as the Nether is below the End.
		if (
			"overworld" == last_dimension or
			   "nether" == last_dimension
		) then
			if vector.distance(
				player_position,
				mcl_vars.mg_end_platform_pos
			) < MAX_DISTANCE then
				return true
			end
		end
		-- Going to the End via the Void is allowed only if
		-- the player entered the Void from the End … nil has
		-- to be handled here for players who were in the Void
		-- when this mod was activated.
		if "void" == last_dimension then
			if (
				"end" == last_last_dimension or
				  nil == last_last_dimension
			) then
				return true
			end
		end
	end
	if "nether" == dimension then
		assert( player_position.y > mcl_vars.mg_nether_min )
		assert( player_position.y < mcl_vars.mg_nether_max )
		-- Going to the Nether through a portal is allowed.
		if "overworld" == last_dimension then
			if nil ~= minetest.find_node_near(
				player_position,
				MAX_DISTANCE,
				"mcl_portals:portal"
			) then
				-- TODO: check for portal in Overworld
				return true
			end
		end
		-- Going to the Nether via the Void is allowed only if
		-- the player entered the Void from the Nether … nil
		-- has to be handled here for players who were in the
		-- Void when this mod was activated.
		if "void" == last_dimension then
			if (
				"nether" == last_last_dimension or
				     nil == last_last_dimension
			) then
				return true
			end
		end
	end
	if "overworld" == dimension then
		assert( player_position.y > mcl_vars.mg_overworld_min )
		assert( player_position.y < mcl_vars.mg_overworld_max )
		-- Going to the Overworld from the Nether through a
		-- portal is allowed.
		if "nether" == last_dimension then
			if nil ~= minetest.find_node_near(
				player_position,
				MAX_DISTANCE,
				"mcl_portals:portal"
			) then
				-- TODO: check for portal in Nether
				return true
			end
			return true
		end
		-- Going to the Overworld via the Void is allowed only
		-- if the player entered the Void from the Overworld …
		-- nil has to be handled here for players who were in
		-- the Void when this mod was activated.
		if "void" == last_dimension then
			if (
				"overworld" == last_last_dimension or
				        nil == last_last_dimension
			) then
				return true
			end
		end
		-- Going to the Overworld via the End (or any other
		-- way) is allowed only if the player appears at their
		-- respawn location, either because they used a portal
		-- in the End or because they died.
		local player_spawn_position = (
			mcl_spawn.get_player_spawn_pos(player) or
			mcl_spawn.get_world_spawn_pos(player)
		)
		if vector.distance(
			player_position,
			player_spawn_position
		) < MAX_DISTANCE then
			return true
		end
	end
	if "void" == dimension then
		-- Going to the Void is always legal – a player who
		-- enters the Void and then goes anywhere else than
		-- where they came from is already handled above.
		return true
	end
	return false
end

local kill_player_for_dimensional_trespassing = function(
	player_name,
	dimension,
	last_dimension,
	last_last_dimension
)
	local player = minetest.get_player_by_name(player_name)
	if nil == player then
		return
	end
	-- If the player holds a totem of undying, destroy it before
	-- killing, so it doesn't rescue the player.
	local wield = player:get_wielded_item()
	if wield:get_name() == "mobs_mc:totem" then
		player:set_wielded_item("")
	end
	local death_message = S(
		"@1 was executed for dimensional trespassing.",
		player_name
	)
	mcl_death_messages.player_damage(
		player,
		death_message
	)
	player:set_hp(0)
	local log_message = string.format(
		"%s was executed for dimensional trespassing: %s → %s → %s",
		tostring(player_name),
		tostring(last_last_dimension),
		tostring(last_dimension),
		tostring(dimension)
	)
	minetest.log(
		"action",
		log_message
	)
end

mcl_worlds.register_on_dimension_change(
	function(player, dimension, last_dimension)
		local player_name = player:get_player_name()
		local last_last_dimension = storage:get_string(
			player_name .. ":dimension_previous_previous"
		)
		if not dimension_change_is_legal(
			player_name,
			dimension,
			last_dimension,
			last_last_dimension
		) then
			kill_player_for_dimensional_trespassing(
				player_name,
				dimension,
				last_dimension,
				last_last_dimension
			)
		end
		storage:set_string(
			player_name .. ":dimension_previous_previous",
			last_dimension
		)
		storage:set_string(
			player_name .. ":dimension_previous",
			dimension
		)
	end
)